This invention relates to apparatus for effecting a cut through a flexible sleeve, such as thin plastics material tubing to form a cut sleeve.
Relatively thin plastics material tubing is used widely in the food processing and other industries for the manufacture of sleeves, either for decorating or labelling a container or for furnishing a container with a tamper-evident device. In the former case, the sleeve is pre-printed with a suitable decorative and informative matter and is then cut to the appropriate length for fitting over the container. Each cut length is then applied to a respective container and secured in position, around the main body of the container. In the latter case, there is no need for the cut length of the sleeve to be decorated in any way and the sleeve does not need to extend over the whole of the container body; it is sufficient for the sleeve to fit over the container closure and the immediately adjacent part of the container body. Such a relatively short sleeve is often referred to as a xe2x80x9cbandxe2x80x9d though for convenience both sleeves and bands will hereinafter be referred to as xe2x80x9csleevesxe2x80x9d and sleeving and banding operations as xe2x80x9csleevingxe2x80x9d.
A sleeve as described above is usually made of heat-shrink plastics material such as of PVC and, prior to shrinking, typically has a thickness in the region of 40 xcexcm. Prior to shrinking, the plastics material is highly flexible and also susceptible to static electrical charges. These properties make it relatively difficult to perform the required operations on the sleeve prior to and as the sleeve is fitted on to a container, especially when high-speed sleeving (at rates in excess of 250 containers per minute) is to be performed.
A particular difficulty of a high-speed sleeving machine adapted to fit sleeves on to containers moved through a sleeving station is the cutting of the required length of sleeve for each container, in a highly reliable manner. Various devices have been proposed for high speed cutting of very flexible plastics material tubing used for sleeves, but these tend to be somewhat cumbersome and difficult to install in the relatively confined space of a sleeving machine, unreliable in operation due to their mechanical complexity and also unable to operate at relatively high speeds. Moreover, on account of various out-of-balance components or on having components which must perform reciprocating actions, these prior designs can introduce undesirable vibrations, which in turn can affect the operation of other components associated with the sleeving machine.
It is an aim of the present invention to provide cutting apparatus suitable for use, for example, with a sleeving machine and which apparatus is able to operate consistently and reliably at relatively high cutting speeds, without adversely affecting a sleeving operation, as a whole.
According to one aspect of the present invention, there is provided cutting apparatus for effecting a cut through flexible tubing slidably supported for advancement on a mandrel having a peripheral groove at the location of the intended cut, which apparatus comprises an annulus co-axially surrounding the mandrel, drive means to rotate the annulus about its axis, a blade carrier pivoted on the annulus about an axis parallel to the annulus axis and supporting a cutting blade movable between withdrawn and cutting positions with respect to said groove by pivoting movement of the carrier, the carrier having an armature portion arranged between a pair of electromagnets mounted on the annulus, and current supply means for the electromagnets whereby the armature portion is attracted selectively to either one of the two electromagnets so that the blade may be held in its withdrawn position by one electromagnet until a predetermined length of tubing has been advanced past the groove in the mandrel whereafter the blade may be moved to its cutting position by energisation of the other electromagnet, to effect a cut through the tubing.
It will be appreciated that with the cutting apparatus of this invention, the annulus is rotated continuously and uni-directionally about its axis, and the annulus supports a cutting blade which is movable between a withdrawn position where the blade is clear of the tubing extending axially through the annulus and supported by the mandrel, and a cutting position where the blade is partially received in a groove in the mandrel, so as to cut through the tubing. Compared to the overall mass of the annulus, the cutting blade and its carrier may have a relatively small mass, and by substantially balancing the carrier about its pivotal axis, with a carried blade on one side of the axis and the armature portion of the other side thereof, the overall rotating mass may be balanced for all operating positions, so minimising vibrations and assisting smooth and reliable operation.
It would be possible for the armature to be of a ferromagnetic material and to energise alternately the electromagnets, depending upon the required position of the cutting blade. However, in a preferred form of the invention, the armature comprises a permanent magnet, advantageously of a low mass, high strength rare-earth magnetic material, and which is simultaneously attracted to one electromagnet and repelled by the other electromagnet, upon simultaneous energisation of both electromagnets. In this case, the two electromagnets may be air-cored so that the magnetic armature is not attracted to either electromagnet when not energised, though the electromagnet to which the armature is attracted when the cutting blade is in its withdrawn position may have a small ferrous core, so as thereby to provide a correspondingly small bias to the carrier, to the withdrawn position of the cutting blade.
In order to allow relatively high speed cutting operations to be performed, it is desirable that the carrier is moved rapidly and reliably, at precisely the required moments, between the withdrawn and cutting positions of the cutting blade. To this end, the current supply means may be arranged to provide a high energy pulse to an electromagnet to which the armature is to be attracted, at the moment the carrier is to be moved, whereafter the supply current may fall back to a lower value so as to maintain the armature adjacent the electromagnet to which it was attracted. In a case where the armature has a permanent magnet and the armature is simultaneously attracted and repelled by the two electromagnets respectively, both electromagnets may be provided with high energy pulses better to ensure rapid movement of the carrier between its two positions.
Rapid penetration of the cutting blade through the material of the sleeve to be cut may be assured by having the blade mounted on its carrier in such a way that on contracting the sleeve, friction between the blade and the sleeve moves the blade deeper into the groove in the mandrel. Thus, on the blade being moved towards its cutting position and starting to effect a cut, this frictional drag will assure continued and reliable cutting of the tubing until a sleeve is wholly severed from the tubing.
The apparatus as described above would operate with just one carrier and cutting blade, a sleeve being severed upon the annulus performing a full turn with the cutting blade in its cutting position. In order to increase the rate at which the cutting apparatus may operate, without having corresponding increases in the rotational rate of the annulus, there may be two or more carriers and cutting blades together with associated electromagnets provided on the annulus. In a preferred embodiment of the apparatus, five such assemblies are provided all of which operate simultaneously in the same sense, whereby a sleeve is wholly severed from an uncut length of the tubing upon the annulus performing 72xc2x0 of arc following initiation of cutting.
The cutting apparatus may be adjustable to suit a wide range of tubing diameters. For each different diameter, an appropriate mandrel must be provided and the bore through the annulus must be sufficient to accommodate that mandrel and the tubing thereof. Each carrier preferably is adjustably mounted on the annulus so that its pivotal connection thereto may be moved substantially radially thereby to adjust the withdrawn and cutting positions of the cutting blade. This may be achieved by providing an adjustment bar which is used to replace the mandrel and each carrier then being adjusted so that its cutting blade, when in its cutting position, just contacts the adjustment bar. Replacement of the adjustment bar by a suitable mandrel having a groove at the cutting position will then permit the cutting of tubing advanced over that mandrel.
This invention extends to a sleeving machine comprising cutting apparatus of this invention and as described above in combination with a mandrel having a peripheral groove at the location of the intended cut, means mounting the annulus co-axially with respect to the mandrel so that a blade when moved to its cutting position lies partially within the groove, feed means to advance the tubing along the mandrel past the groove therein, removal means to move a cut length of tubing (a sleeve) off the mandrel and on to an item to be sleeved, and control means to cause a predetermined length of tubing to be advanced past the groove, to effect cutting of the advanced length of sleeve by suitable energising of the electromagnetic, and to cause the removal means to operate in a timed relationship to advancement of an item to be sleeved past the end of the mandrel.
In the sleeving machine as just described, the removal means may comprise a continuously-running pinch roller arrangement disposed beyond the free end of an advanced length of tubing ready to be cut off, said free end being moved into the pinch roller arrangement after the advanced length has been cut off upon operation of the feed means to advance a further predetermined length of tubing ready for cutting, the cut off sleeve being moved by engagement of its trailing end with the advancing end of the uncut tubing. The pinch roller arrangement should run at a relatively high speed, so that as soon as the free end of the cut sleeve enters the pinch roller arrangement, that sleeve is moved away much more rapidly than the advancing tubing.
As in a conventional sleeving machine, the free end of the mandrel should overlie the path along which articles to be sleeved are advanced, whereby the cut sleeve are applied directly on to the articles. Thus, the advancement of the tubing must be in a timed relation to the advancement of the articles to be sleeve along the path, to ensure that each cut sleeve is applied properly to the articles, on being moved by the pinch roller arrangement. However, it would be possible to use an intermediate mandrel arrangement, in a manner known in the art, and on to which the cut sleeves are moved prior to being applied to the articles.
By way of example only, one specific embodiment of cutting apparatus and a sleeving machine constructed and arranged in accordance with the present invention will be now described in detail, reference being made to the accompanying drawings, in which:
FIG. 1 is a diagrammatic under plain view of the embodiment of cutting apparatus:
FIG. 2 is a detail view on an enlarged scale of a carrier and cutting blade assembly, as used in the apparatus of FIG. 1;
FIG. 3 illustrates the adjustment of the carrier to suit different tubing diameters;
FIG. 4 is a diagrammatic front view of a sleeving machine incorporating cutting apparatus of this invention;
FIG. 5 is a plan view of the sleeving machine of FIG. 4; and
FIG. 6 is a circuit diagram of the drive arrangement for the electro-magnets used in the cutting apparatus.